The present invention concerns a drill bit for hand drills which has a clamping shank for attachment to a hand drill and a drill shank having at least one cutting edge and at least one chip-removal groove.
The known hand drills can be divided into three groups, namely into hammer drills, percussion drills and ordinary drills, their practical importance decreasing in the sequence indicated.
A hammer drill is a drill in which the bit is held within a tool holding fixture or chuck in such a manner that it is movable axially but is keyed for the transmission of the rotation of the holding fixture or chuck to the bit. In a hammer drill, an impact pin also known as hammer is provided which is moved axially back and forth and is adapted to exert blows on the rear end of the bit's clamping shank which is clamped in the holding fixture or chuck of the hammer drill.
In percussion drills, the chuck is attached to an axially movable spindle on which blows are exerted during the drilling so that the chuck is moved axially back and forth together with the bit, which is clamped firmly in it.
In ordinary drills, the bit is merely imparted a rotating movement so that the bit, which is clamped in the drill and rotates, must be pressed into the drill hole.
In the hammer drills which are customary on the market the tool-holding fixtures all have the same diameter, so that the bits for holes of different diameter must always have a clamping shank of the same diameter, which greatly increases the cost of manufacture of the bits.
As compared with this, percussion drills and ordinary drills have three-jaw chucks in which the chucks can be adapted to different diameters of the clamping shanks so that in the bits used in these drills the diameters of the cylindrical surface of the drill shank and of the clamping shank are substantially the same.
From Federal Republic of Germany OS No. 31 18 691 a hammer drill is known in which a multiple-jaw chuck, for instance a three-jaw chuck, can also be used for the clamping of the bit, so that it is possible to use in these hammer drills also bits in which the diameter of the bit shank and of the clamping shank is substantially the same.
For the keyed transmission of the torque from the tool-holding fixture or chuck to the bit it is known in the case of hammer drills to provide axially extending grooves in the clamping shank of the bit, driving parts of the chuck engaging in said grooves so that the bit, which is held with limited axial movement in the tool-holding fixture or chuck for the transmission of the blows to the place of drilling is driven along in keyed fashion by the engagement of the driving parts into the grooves upon the rotation of the chuck.